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An electrical device which has the property to oppose the current passing through it is known as resistor, or a device which resist the current passing through it. Now days different types of resistors are used to regulate the current of desired value in every electrical and electronics circuit. The unit for measuring resistance is the OHM. (The Greek letter Ω - called Omega).Higher resistance values are represented by "k" (kilo-ohms) and M (mega ohms). For example, 120 000 Ω is represented as 120k, while 1 200 000 Ω is represented as 12M.
OHM's Law :
When a potential difference is applied between the ends of a conductor, current begins to flow through it. George Simon Ohm, a German physicist performed a series of experiment to determine the exact relationship between the potential difference and electric current. On the basis of these experiments he formulated a law which is called a ohm's and can be stated as,the potential difference(V) applied between the ends of a conductor bears a constant ratio with the electric current(I) flowing through it, provides the physical state of the conductor remains the same.The factors which constitute physical state of conductor are its length, area of cross section, temperature and material.According to ohm's law
V directly propotional to I
V/I=constant
The constant in the above relation is called resistance(re) of the conductor.
V/I=R OR V=I*R
Resistance Colour Code:
In electronic circuit the value of resistance is determined by their colour code as shown in figure :| Color | 1st Band | 2nd Band | Multiplier | Tolerance |
|---|---|---|---|---|
| Black | 0 | 0 | 1E | |
| Brown | 1 | 1 | 10E | +1%F |
| Red | 2 | 2 | 100R | +2%G |
| Orange | 3 | 3 | 1KE | |
| Yellow | 4 | 4 | 10KE | |
| Green | 5 | 5 | 1ME | +0.5% |
| Blue | 6 | 6 | 10ME | +0.25% |
| Violet | 7 | 7 | +0.10% | |
| Grey | 8 | 8 | +0.05% | |
| White | 9 | 9 | ||
| Gold | 0.1 | +5%(J) | ||
| Silver | 0.01 | +10%(K) |
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